Dynamic Modelling and Validation of an Air-to-Water Reversible R744 Heat Pump for High Energy Demand Buildings

This paper presents a reversible heat pump based on CO2 as the refrigerant, able to provide heating, cooling, and domestic hot water to high energy demand buildings. The unit was developed and tested under the EU H2020 project MultiPACK, which has the main goal of assuring the market about the feasibility, reliability, and energy efficiency of CO2 integrated systems for heating and cooling and promoting a fast transition to low environmental impact solutions. Within the project, the confidence raising was performed by installation and monitoring of fully integrated state-of-the art CO2 systems in the Southern European Climate. With the aim of predicting the unit behaviour under variable load and boundary conditions, a dynamic model of the entire unit was developed with commercial software, considering actual components and the implemented control system and it was validated with experimental data, collected at the factory’s lab before commissioning. The validation against experimental data collected during operation as a heat pump demonstrated a maximum percentage difference between the experimental and predicted value of gas–cooler heat flow rate equal to +5.0%. A preliminary comparison with the experimental data in chiller configuration is reported, however further development was required to achieve a satisfactory validation. Lastly, the numerical model was utilized to simulate a typical operation in heat pump configuration with the system coupled with a hot water tank storage for the production of domestic hot water and space heating; the model predicts higher COP when operating in domestic hot water operation due to the lower water inlet temperature.

Domestic Hot Water Consumption Profiles Applied to a Flat Tubular Collector for Solar Water Heating in Bogotá

The use of Flat Solar Collectors for the generation of Domestic Hot Water (DHW), facilitates access to this resource in an efficient, economical and sustainable way. The Sustainable Development Goals proposed by the UN, referring specifically to sustainable water management and access to renewable energy, are the main motivation for this work, since the former is an essential vital resource and its access reduces the inequality index, in developing countries such as Colombia, while the use of solar thermal energy reduces the environmental impact of the water heating process, thus reducing the consumption of electrical energy in the residential sector. Therefore, this work proposes to estimate DHW profiles through a spreadsheet that models the DHW flow thermodynamically for a whole year, making it possible to evaluate the energy performance of a Solar Collector available in the Colombian market and that is used in four types of dwellings located in the city of Bogotá. The simulation results present the DHW consumption profiles in kg/h per year, with DHW temperatures of up to 21°C, for a total transmitted irradiance of the order of 1100 W/m^2, which produces thermal energy close to 1kW. This comparative analysis allows us to review the technical and economic feasibility of solar collectors installed in single-family homes and with a DHW consumption profile close to the Colombian socio-economic reality.